Panasonic radio--buzzing buzzing!

My Prostar factory radio had a bad input jack (for the XM radio), so the shop ordered a Panasonic and replaced it. That's good, but now when I listen to the XM radio through the new Panasonic input jack, there is a lot of buzzing, that revs up and down with the engine. I really hate to bug the shop guys again, they will probably tell me there is nothing they can do. Any suggestions? I would take it to a radio shop, somewhere between Houston and Chicago, if I could find one that knows this stuff.

 

Hi and thanks for the replies. I have more info: I found that the buzzing only occurs using the input jack for the XM radio. USB? CD? FM radio? No buzzing. I can set the source for AUX (which is the XM radio input jack) and the buzzing occurs when the XM radio is on. If I turn off the XM radio, buzzing stops. I'm guessing the problem is, the radio is sensitive and is picking up the noise through the XM radio. I have ordered a PAC isolator like this:

I will let you know if that works!

 

This worked perfectly~